"Abbott Formation" "Abernathy Member" "Abingdon Coal Member" "Absaroka Sequence" "Afton Soil" "Alburnett Formation" "Alexandrian Series" "Allard Limestone Member" "Allenby Coal Member" "Alto Formation" "Ancell Group" "Anna Shale Member" "Antioch Limestone Member" "Anvil Rock Sandstone Member" "Argyle Till Member" "Arsenal Member" "Ashmore Tongue" "Assumption Coal Member" "Athensville Coal Member" "Atokan Series"